Ali Rezaian, brother of Jason Rezaian, arrives at a July 22 news conference in Washington where reporters were given an update on the incarcerated Post reporter’s case. (Molly Riley/Associated Press)

AMERICANS ARE asking the extent to which Iran can be trusted — in its arms control commitments, its regional behavior and its treatment of foreign investors.

One way to answer that question is to examine the extent to which Iran’s regime obeys its own laws, on which subject several United Nations human rights experts had some relevant things to say on Friday. They were examining the unjust incarceration of Post reporter Jason Rezaian, and their conclusions were stark. “He has suffered unlawful treatment during his year-long incarceration,” said Seong-Phil Hong, who heads the U.N. Working Group on Arbitrary Detention.

Mr. Rezaian has been held in Tehran’s infamous Evin prison since his arrest on July 22, 2014. This alone would appear to violate Iranian law, which says no suspect may be held for longer than a year unless accused of murder. The charges against Mr. Rezaian have never been made public, but according to his lawyer they do not include homicide. Apparently they center instead on what the State Department has called “patently absurd” allegations of espionage and aiding a hostile government, though it’s hard to know: His “trial” has been conducted in secret, with not even his relatives allowed to attend, and no live witnesses or substantial evidence have been presented.

“Mr. Rezaian seems to have been detained for the simple fact of having exercised his rights to freedom of expression, association and political participation,” Mr. Hong said. “His rights to legal counsel of his choice and to due process of law seem to have been forgotten.”

A second U.N. expert, David Kaye, the U.N. special rapporteur on freedom of opinion and expression, also sharply criticized Iran’s handling of the Rezaian case. “The arrest, detention and secret trial of Mr. Rezaian violate his rights and intimidate all those working in the media in Iran,” said Mr. Kaye. “His continued detention violates basic rules that not only aim to protect journalists, bloggers, human rights activists and others but to guarantee everyone’s right to information.”

Both experts, along with Ahmed Shaheed, the U.N. special rapporteur on the situation of human rights in Iran, urged Mr. Rezaian’s prompt release, along with that of “all those exercising their rights to expression who have been arbitrarily arrested, detained and prosecuted.”

Indeed, it is the highly arbitrary treatment of Mr. Rezaian and the disregard of the law that ought to concern everyone weighing the proper contours for future relations with Iran. Conversely, Iranian authorities, who reportedly may issue a verdict in the Rezaian case as early as Monday, ought to keep in mind how anything but immediate release and exoneration will affect their standing in the world.